Planographic printing plate

ABSTRACT

A planographic printing plate comprising a base having adhered thereto an insolublized coating, including a pigment mixture containing zirconium silicate so as to enhance rejection of ink in nonimaged areas of the plate

I United States Patent [151 3,640,22 1 Wyke Feb. 8, 1972 [54]PLANOGRAPHIC PRINTING PLATE 2,814,988 12/1957 Bradstreet et a1 ..101/4582,964,403 12/1960 Beekman et a1. ....1 17/152 X m] Edward wyke ChelmsfmdMass 3,169,865 2/1965 Wood ....117/152 x Assignee: Litton us n Systems,New ork, 3,254,597 6/1966 Hart 61:51.. ..101/462 NY. 3,455,241 7/1969Perkins ..101/462 X 3,508,952 4/1970 Eykamp ..117/152 x 1 d. F b. 111970 [22] e e 3,557,696 1/1971 Hoover et al. ..101/462 x [2]] Appl. No.:10,634

Primary Examiner-David Klein 52 u.s.c1 ..101/453,117/152,101/460,Attorney-Norma" Friedman, Stephen E Feldman, Morris [01/462 Pollack,Arthur T. Groeninger and Philip Furgang [51] Int. Cl. ..B41n 1/00, B41n3/00 [58] Field ofSearch ..117/152; 101/460, 462, 458, ABSTRACT 101/453A planographic printing plate comprising a base having adhered theretoan insolublized coating, including a pigment [56] References Citedmixture containing zirconium silicate so as to enhance rejec- UNITEDSTATES PA'I-ENTS tion of ink in nonimaged areas of the plate 2,542,7842/1951 Van Dusen 101/460 2 Claims, No Drawings PLANOGRAPIIIC PRINTINGPLATE BACKGROUND OF THE INVENTION Planographic printing plates are madeby applying to a base web or sheet a coating having, among other things,desirable hydrophilic-oleophilic properties whereby a greasy compositionmay be retained, to form an ink-receptive image, and an aqueous etch orfountain solution may be retained by the remainder of the plate to forman ink-repellent surface. Such plates may be mounted on a roller of anoffset printing press, for example, and caused to pass successively incontact with a fountain solution and a printing ink. Ideally, the ink istotally rejected by the plate due to the fountain solution, except forthe imaged areas thereof to which the ink adheres due to the absence ofthe fountain solution. The inked image is then transferred to a blanket,for image reversal, and applied to the sheet to be printed.

In the past, the ink has not been completely rejected in the nonimagedareas.

BRIEF DESCRIPTION Broadly, the improved planographic printing plate ofthis invention is prepared by forming an aqueous coating compositioncomprising a novel clay pigment mixture including zirconium silicate.Conventional components in the composition.

. DETAILED DESCRIPTION Various known coating grades of filler clays canbe used to form the pigment mixture according to this invention. Claysof small particle size are preferred since they seem to produce betterresults. Some examples of clays which can be used include various typesof kaolin or china clays, Lustra Clay and so forth. Lustra Clay,marketed by the Southern Clay Company, has been found to be particularlyadvantageous. No. l Hydrofine, marketed by Georgia Koalin Company hasalso been found to be particularly advantageous.

The zirconium silicate utilized should have a particle size less than 40microns and preferably less that 4 microns. There is no lower limit asthe smallest particles commercially available, i.e., 0.15 microns hasproved feasible. The ratio of clay to zirconium silicate may vary widelyfrom about 20 to l to about 1 to 1, depending upon the propertiesdesired in the finished late. p Although it is preferred to use a clayalong with the zirconium silicate in the pigment mixture, other pigmentsmay be used in place of, or in addition to, the clay, such as calciumsilicate, barium sulfate, titanium dioxide, etc.

If desired, dispersing agents maybe employed along with these pigmentmixtures, such as sodium hexametaphosphate, disodium dihydrogenpyrophosphate, tetrapostassium pyrophosphate, tetrasodium pyrophosphate,etc.

Polyvinyl alcohol is preferably used as the adhesive. The higher themolecular weight and the greater the polyvinyl alcohol is hydrolized,the greater the ease of insolubilization. Polyvinyl alcohol is generallyobtainable and applied in aqueous solution. Various commercial gradesare suitable for the purpose, such as Elvanol manufactured by E. l. duPont de Nemours and Company.

There is an optimum ratio of pigment mixture to adhesive and experimentsindicate that overall the pigment/adhesive ratio should preferably bebetween about 9 to l and 4 to l Advantageously, the cross-linking agentused in the composition is glyoxal, and the ratio of the cross-linkingagent to the adhesive may advantageously be from approximately 10 to 70percent, and preferably 35 percent, based on the adhesive.

Other suitable cross-linking agents can be used, such asureaformaldehyde, N,N'-ethylene dimethylol cyclic urea,

dimethylol urea, other dialdehydes, etc.

Zin'c acetate may be added. This enters the pores and the intersticesexisting among adjacent particles of mineral pigment in coating, andafter evaporation of the aqueous vehicle the dry but still soluble saltremains deposited and partially fills the pores and interstices. Whenthe surface is subsequently treated with an aqueous lithographic wetoutof fountain solution which contains an ingredient capable of reactingwith said soluble zinc acetate to form a less soluble or insolublecompound, such as an insoluble or slightly insoluble compound of thezinc acetate, is formed inside of the pores and interstices of thecoating. The insoluble or slightly soluble multivalent zinc acetatecompound so formed acts to plug the pores and interstices and to aconsiderable extend prevents or decreases further penetration of thesurface by the lithographic solution. The optimum ratio of zinc acetateshould preferably be between about 5 to 15 percent of the total solidspresent in the coating;

The'hydrochloric acid is added to the composition in suffrcient quantityto bring it down to a pH range of 3 to 5.5. Hydrochloric acid may beadded to the composition prior to the addition of zirconium silicateand/or zinc acetate.

If desired, a plasticizer such as glycerin may be added to thecomposition so as to enhance the flexibility of the plate.

The following examples illustrate the manner of preparing the improvedplanographic plates of this invention in more detail. The followingcoating composition mixtures were prepared and coated on a base paperand dried. The resulting planographic printing plates had low waterabsorbency and possessed an excellent hydrophilic-oleophilic balance,permitting good image adherence and good image life while at the sametime permitting good water retention. These plates produced clean copy,good toning, and possessed good image, correction of life, and stop-goproperties. Parts are by weight, zirconium silicate had a particle sizeranging from 0.l5 to 4 microns.

Zinc acetate In each of the above, the clay and zirconium silicate areadded to water to form a 50 percent solid dispersion. A 10 percentaqueous solution of polyvinyl alcohol is then added to the pigmentdispersion. Acid was then added to provide a pH 0.2 to 515. A 40 percentaqueous solution of glyoxal was then added followed by the addition of a20 percent solution of zinc acetate? Tests of sheets prepared accordingto the above indicated that the proportions listed in mixtures A, B andC were best. Mixture'D had poor press characteristics due to backgroundtone. Mixtures A, B, and C greatly improved background cleanliness.Mixture C provided best performance.

The coating composition may be applied to the base web sheet byconventional apparatus, such as air knives or roll coaters.-'The amountof coating may vary from abo i 5 to 20 lb. per 3-,300 sq. ft. Aftercoating, the stock is dried nd cured at a suitable temperature.Temperature as low as F. and as high as 320 F. have been used. Thecuring time will vary directly with the amount of heat applied. Thecoating composition is self-insolubilizing and the components reactduring the drying/curing cycle to produce a practically water-imperviousfilm, which possesses excellent properties of accepting and holding bothwater and greasy ink.

surface comprising a pigment mixture and the reaction product of ahydrophillic colloidal adhesive and a cross-linking agent, said pigmentmixture containing zirconium silicate.

2 The planographic printing plate of claim 1, in which the zirconiumsilicate has a particle size of between 0.15 and 4 microns.

2. The planographic printing plate of claim 1, in which the zirconiumsilicate has a particle size of between 0.15 and 4 microns.